1. Technical Field
This invention pertains to the control of a simulated moving bed (SMB). It is particularly directed to a block displacement procedure which may be applied, for example, to recover a betaine fraction from the circulation loop in an SMB of a sugar factory.
2. Background Art
U.S. Pat. No. 4,412,866 describes the operation of an SMB to separate the components of a feed stock. A resin bed is divided into a series of discrete vessels, each of which functions as a zone within a circulation loop. A manifold system connects the vessels and directs in appropriate sequence to each vessel each of the four media accommodated by the process; namely, feed stock, eluant, extract and raffinate. As applied to a sugar factory, a typical feed stock is sucrose solution, the eluant is water, the extract is an aqueous solution of sucrose and the raffinate is an aqueous solution containing nonsucrose, such as salts and high molecular weight compounds
The largest single loss of sugar values from a typical sugar factory is attributable to molasses formation. Molasses comprises the byproduct (or waste) stream remaining after repeated crystalizations to recover purified sugar. This molasses is typically of such low purity that further crystallization procedures for the recovery of additional sugar are economically impractical. SMB arrangements similar to those disclosed by the '866 patent are used in sugar factories to process molasses; typically producing a product fraction of relatively high (e.g., 90%) purity and low ash content and a waste fraction, comprising 40-50% of the feed, of relatively low purity and high ash content. (As used in the sugar industry, "purity" specifies percent by weight sucrose of the solids contained in a sample, on a dry weight basis.) This waste fraction contains most of the betaine values of the molasses feed. Betaine, being the most abundant nitrogenous compound found in molasses, has been recognized as a commercially useful byproduct; notably for use in animal feeds.
U.S. Pat. No. 4,359,430 and 5,127,957 describe methods for the recovery of a betaine fraction from various sources, such as the molasses produced by a sugar factory. The '957 patent discloses a batch operation imposed upon an SMB system. The method involves shutting off all input and output streams to the SMB while maintaining circulation through the resin bed. Thereafter, water and/or molasses feed are introduced to displace betaine, sucrose and rest molasses from separate columns in the loop.
There remains a need for an improved method for the recovery of betaine from an SMB system. Ideally, betaine removal should be accomplished without disrupting the continuous operation of the system.